The Aitoliko Lagoon (Greek: Λιμνοθάλασσα Αιτωλικού Limnothalassa Aitolikou) is a lagoon located in the south of Aetolia-Acarnania, Greece. It is separated from the larger Messolongi Lagoon (a bay of the Gulf of Patras) to the south by the island of Aitoliko. Its maximum depth is 28 metres. At a salinity of 19-28 PSU, its water is brackish. Oxygen depletion occurs in a large part of the lagoon, but has been reduced since 2002 by creating larger openings around Aitoliko island and dredging channels in Messolongi Lagoon.